Method and apparatus for transmitting channel measurement information in mobile communication system

ABSTRACT

A method and apparatus for transmitting channel measurement information in a mobile communication system are disclosed. The method and apparatus enable a user equipment to log channel measurement information and transmit the same to a base station so as to enhance radio network performance and reduce processing complexity of the user equipment by removing unnecessary operations of the user equipment and preventing waste of radio network capacity during transmission of channel measurement information.

TECHNICAL FIELD

The present invention relates to transmission of channel measurementinformation in a mobile communication system and, more particularly, toa method and apparatus in a mobile communication system that enable auser equipment to log channel measurement information and transmit thesame to a base station so as to enhance radio network performance andreduce processing complexity of the user equipment by removingunnecessary operations of the user equipment and preventing waste ofradio network capacity during transmission of channel measurementinformation.

BACKGROUND ART

In general, mobile communication systems have been developed to providecommunication services to users in motion. Thanks to rapid technicaladvancement, mobile communication systems are capable of providing notonly voice communication services but also high-speed data communicationservices.

Recently, 3GPP has been working to standardize specifications for theLong Term Evolution-Advanced (LTE-A) system, which is regarded as a nextgeneration mobile communication system. The LTE-A system is expected tobe standardized in late 2010, and aims to realize high-speed packetbased communication supporting a data rate higher than existing ones.

As 3GPP standards evolve, schemes for efficient radio networkoptimization are proposed. Generally in initial radio network deploymentor optimization, the operator of a base station or base stationcontroller has to collect radio environment information related to cellcoverage though drive tests. In existing drive tests, a measurer isinconvenienced by having to drive a car loaded with measurementinstruments along the road for a long time in a repetitive way.Measurement results are analyzed and used to set system parameters forthe base station or base station controller. Such drive tests increaseoptimization and operating costs of radio networks and are timeconsuming. As such, a study named MDT (Minimization of Drive Tests) isin progress to reduce manual drive tests and enhance the process ofradio environment analysis and parameter setting. Instead of performingdrive tests, a user equipment (UE) performs channel measurement and logsthe channel measurement information. Then, the user equipment mayimmediately send the channel measurement information to the basestation, send the same in response to occurrence of a particular event,or send the same after expiration of a preset time. Hereinafter,transmission of channel measurement information collected by the userequipment to the base station is referred to as channel measurementinformation reporting or MDT measurement information reporting. The userequipment may immediately send channel measurement results when it iscommunicable with the base station, or may save the channel measurementresults and send the same later when it become communicable with thebase station.

The base station uses the channel measurement information received fromthe user equipment to optimize cell coverage. In LTE-A, MDT measurementinformation reporting is basically classified by UE RRC state asfollows.

TABLE 1 UE RRC state Basic MDT measurement information reporting of UEIdle mode Logging and deferred reporting Connected mode Immediatereporting Connected mode Logging and deferred reporting

MDT measurement information reporting according to UE RRC state

Referring to Table 1, idle mode indicates a state in which the userequipment is not in communication with the base station, and connectedmode indicates a state in which the user equipment is in communicationwith the base station. For MDT, as channel measurement informationcollected by the user equipment is transmitted through RRC signaling,the user equipment in idle mode is not required to transition toconnected mode. In this case, the user equipment logs the collectedchannel measurement information and defers transmission of the sameuntil transitioning to connected mode.

In connected mode, the user equipment may immediately send channelmeasurement information to the base station according to circumstancesor may log the channel measurement information and send the same lateras in idle mode.

In idle mode, the user equipment logs channel measurement information onan event basis or on a periodic basis. Examples of events triggeringlogging of channel measurement information are listed below.

(1) Periodic downlink pilot measurements

(2) Serving cell becomes worse than threshold

(3) Transmit power headroom becomes less than threshold

(4) Paging channel failure

(5) Broadcast channel failure

(6) Random access failure

(7) Radio link failure report

Logging events (1), (2), (4), (5) and (7) may be used to optimizedownlink cell coverage, and logging events (3) and (6) may be used tooptimize uplink cell coverage. The event (1) is related to periodiclogging of channel measurement information, and the other events arerelated to logging of channel measurement information when a givencondition is satisfied. The logged channel measurement information isreported to the base station when the user equipment transitions toconnected mode. The user equipment may also log channel measurementinformation in connected mode.

The user equipment in connected mode sends logged channel measurementinformation to the base station when a reporting event is triggered.Currently, various report triggering conditions are considered instandard meetings. As channel measurement information for MDT is neededby the base station, a report request made by the base station (ondemand) and a report trigger sent by the user equipment to the basestation are considered as a report triggering condition.

As MDT procedures are not clearly determined, it is necessary to definean optimized MDT procedure.

For the purpose of MDT, an MDT procedure will be carried out duringinitial deployment and optimization of a radio network. That is, it issufficient to conduct MDT only for a particular duration. Hence, it isnecessary to notify the user equipment of the time to conduct MDT. Inaddition, it is unnecessary to handle the logging events proposed atstandard meetings in all RRC states. For example, as it is possible tomeasure power headroom only in connected mode, the logging event (3) mayoccur only in connected mode. Hence, it is necessary to define a loggingevent on a mode basis in consideration of usefulness and ease ofimplementation. Transmission of channel measurement information from theuser equipment to the base station may result in reduction of uplinkcapacity for other data transfer. Hence, to prevent waste of radioresources, it is preferable to allow the base station to selectivelyrequest only necessary information from the user equipment. Inparticular, a large amount of channel measurement information will belogged when the user equipment remains in idle mode for a long time.Upon transitioning to connected mode, the user equipment may consume alot of resources to send the logged channel measurement information.Accordingly, MDT procedures are to be developed in consideration of theabove problems.

DISCLOSURE OF INVENTION Technical Problem

The present invention has been made in view of the above problems, andthe present invention provides a method and apparatus in a mobilecommunication system that enable a user equipment to log channelmeasurement information and transmit the same to a base station in amanner that enhances radio network performance and reduces processingcomplexity of the user equipment.

The present invention also provides a method for operating a userequipment and a base station that removes unnecessary operations of theuser equipment and prevents waste of radio network capacity duringtransmission of channel measurement information.

Solution to Problem

An aspect of the present invention is to provide a method oftransmitting channel measurement information for a user equipment in amobile communication system, including: receiving MDT configurationinformation from a corresponding base station; performing, upontransitioning to idle mode, MDT measurement for channel status accordingto the MDT configuration information and logging MDT measurementinformation; sending, upon transitioning to connected mode, a flagindicating presence of the logged MDT measurement information to thebase station; and sending, upon reception of a report request from thebase station, the MDT measurement information to the base station.

Preferably, transmission of the MDT measurement information is performedwith a lower priority than transmission of regular data. To achievethis, sending the MDT measurement information to the base station mayinclude: establishing a radio bearer having a lower priority than thatof a radio bearer for regular data; and transmitting the MDT measurementinformation via the established radio bearer.

Another aspect of the present invention is to provide a user equipmenttransmitting channel measurement information in a mobile communicationsystem, including: a transceiver receiving MDT configuration informationfrom a corresponding base station and sending MDT measurementinformation to the base station; a buffer storing collected MDTmeasurement information; and a controller controlling a process ofperforming, upon transitioning to idle mode, MDT measurement for channelstatus according to the MDT configuration information and logging MDTmeasurement information in the buffer, sending, upon transitioning toconnected mode, a flag indicating presence of the logged MDT measurementinformation to the base station, and sending, upon reception of a reportrequest from the base station, the MDT measurement information to thebase station.

Another aspect of the present invention is to provide a method ofreceiving channel measurement information for a base station in a mobilecommunication system, including: sending MDT configuration informationnecessary for MDT measurement to a user equipment; receiving indexinformation of MDT measurement information from the user equipment, anddetermining necessity of the MDT measurement information; and sending,when the MDT measurement information is necessary, a report request forthe MDT measurement information to the user equipment.

Another aspect of the present invention is to provide a base stationreceiving channel measurement information in a mobile communicationsystem, including: a transceiver sending MDT configuration informationto a corresponding user equipment and receiving MDT measurementinformation from the user equipment; and a controller controlling aprocess of receiving index information of MDT measurement informationfrom the user equipment, determining necessity of the MDT measurementinformation, and sending, when the MDT measurement information isnecessary, a report request for the MDT measurement information to theuser equipment.

Advantageous Effects of Invention

In a feature of the present invention, a user equipment may help toenhance radio network performance with reduced processing complexityduring logging of channel measurement information and transmissionthereof to a base station. In addition, waste of radio network capacitymay be prevented by removing unnecessary operations of the userequipment during transmission of channel measurement information.

BRIEF DESCRIPTION OF DRAWINGS

The objects, features and advantages of the present invention will bemore apparent from the following detailed description in conjunctionwith the accompanying drawings, in which:

FIG. 1 is a sequence diagram illustrating a procedure for reportinglogged channel measurement information by a user equipment in responseto a report request from a base station according to a first embodimentof the present invention;

FIG. 2 is a sequence diagram illustrating a procedure for reportingchannel measurement information by a user equipment to a base station inresponse to satisfaction of a report triggering condition according to asecond embodiment of the present invention;

FIG. 3 is a flow chart illustrating steps performed by the userequipment conducting MDT operation;

FIG. 4 is a flow chart illustrating steps performed by the base stationconducting MDT operation;

FIG. 5 is a sequence diagram illustrating a procedure for reportingchannel measurement information in which a user equipment notifies abase station of collected channel measurement information and sends thechannel measurement information according to a report request from thebase station according to a third embodiment of the present invention;

FIG. 6 is a sequence diagram illustrating a procedure for reportingchannel measurement information derived from the procedure of FIG. 5 byreplacing a two-step report requesting operation with a single-stepoperation according to a fourth embodiment of the present invention;

FIG. 7 is a sequence diagram illustrating a procedure for reportingchannel measurement information in which a user equipment notifies abase station of collected channel measurement information using twoflags and sends the channel measurement information according to areport request from the base station according to a fifth embodiment ofthe present invention;

FIG. 8 is a block diagram of a user equipment conducting MDT operation;and

FIG. 9 is a block diagram of a base station conducting MDT operation.

MODE FOR THE INVENTION

Hereinafter, exemplary embodiments of the present invention will bedescribed with reference to the accompanying drawings.

The present invention relates to a method and apparatus in a mobilecommunication system that enable a user equipment to log channelmeasurement information and transmit the same to a base station in amanner that enhances radio network performance and reduces processingcomplexity of the user equipment. The present invention also relates toan operation method for a user equipment and a base station that removesunnecessary operations of the user equipment and prevents waste of radionetwork capacity during transmission of channel measurement information.

In the present invention, an efficient MDT procedure is defined.

In particular, the method of the present invention includes loggingchannel measurement information by a user equipment in idle mode, andreporting the same in connected mode. The MDT procedure of the presentinvention includes a set of steps related to a direction of the basestation indicating the time to perform MDT, definitions of MDTmeasurements and basic MDT operations that can be carried out accordingto RRC states, transmission of MDT measurement information with a lowerpriority than regular data, and permission of MDT reporting.

In the first embodiment of the present invention, the user equipmentreports logged MDT measurement results only when the base station issuesa report request. In the description, MDT measurement refers to channelmeasurement performed by the user equipment, and MDT measurement resultsare logged as MDT measurement information. MDT measurement informationand channel measurement information may be used interchangeably. In thiscase, the base station may receive an advance notice indicating thecontent of logged MDT measurement results from the user equipment beforedetermining whether to issue a report request to the user equipment.

In the second embodiment, the user equipment reports logged MDTmeasurement results to the base station when a trigging condition issatisfied. As the user equipment may report MDT measurement resultswithout a report request, the base station may reject the report if thereport is regarded as unnecessary.

In the third to fifth embodiments, the user equipment logs MDTmeasurement results and notifies the base station of the presence ofchannel measurement information. Later, the user equipment reports theMDT measurement information in response to a report request from thebase station.

Hereinafter, a description is given of the first to fifth embodiments ofthe present invention.

First Embodiment

FIG. 1 is a sequence diagram illustrating a procedure for reportinglogged channel measurement information by a user equipment (UE) 105 inresponse to a report request from a base station (eNB) 110.

To communicate with the base station 110, the user equipment 105triggers random access (115) and invokes a random access procedure(120). The base station 110 then enters into connected mode (125). Thebase station 110 sends an RRCConnectionReconfiguration messagecontaining MDT configuration information (information necessary toperform MDT) to the user equipment 105 (130). The MDT configurationinformation may include information regarding the time to conduct MDTmeasurement, the frequency and cell to be measured, and logging andreporting. An example of MDT configuration information is given below.

(1) Measurement objects: information regarding a frequency band and cellto be measured by the user equipment

(2) Logging configurations: information on logging events, composed oflogging criteria and logging format

-   -   Logging criteria: criteria triggering UE MDT measurement (refer        to 3GPP TR36.805 for more details)        -   Periodic downlink pilot measurements        -   Serving cell becomes worse than threshold        -   Transmit power headroom becomes less than threshold        -   Random access failure        -   Paging channel failure        -   Broadcast channel failure        -   Radio link failure report    -   Logging format: information on format related to logging        information (refer to 3GPP TR36.805 for more details)

(3) MDT reporting configurations: information regarding MDT measurementreporting by the user equipment, composed of reporting criteria andreporting format

-   -   Reporting criteria: criteria triggering UE reporting        -   On demand: reporting upon request from the base station        -   Absolute time based: reporting at preset time        -   Periodic timer based: periodic reporting        -   UE leaves logging campaign: reporting at MDT stop        -   Location based: reporting at specific location        -   UE memory usage based: reporting when UE memory buffer is            full        -   Combined triggers: combination of above criteria        -   Other    -   Reporting format: information on format related to reporting        information

(4) MDT start/stop configurations: information regarding MDT measurementtime

For the purpose of MDT, MDT measurement is carried out at initialdeployment of a radio network and optimization thereof. That is, it issufficient to conduct MDT only for a particular duration. Hence, it isnecessary for the base station 110 to notify the user equipment 105 ofthe time to conduct MDT measurement. When the user equipment 105 is inconnected mode, the base station 110 may directly signal the MDT stoptime. When the user equipment 105 is in idle mode, as the base station110 may be unable to directly signal the MDT stop time, the base station110 may notify timer information to the user equipment 105 in advance sothat the user equipment 105 stops MDT measurement upon timer expiration.Hence, the user equipment 105 immediately stops MDT measurement when anMDT stop signal is received from the base station 110 before expirationof the timer. Otherwise, the user equipment 105 continues MDTmeasurement and stops MDT measurement upon expiration of the timer.

(5) MDT measurement identities: information regarding parameterscombining the above configuration variables, and corresponding toexisting RRC measurement

(6) Quantity configurations: filtering information related tomeasurement, and corresponding to existing RRC measurement

As a reply to the RRCConnectionReconfiguration message, the userequipment 105 sends an RRCConnectionReconfigurationComplete message tothe base station 110 (135). The user equipment 105 enters into idle mode(140) and starts MDT measurement at the MDT start time (145). MDTconfiguration information may also be transported through anRRCConnectionRelease message that is sent by the base station to theuser equipment before RRC connection release. In other words, MDTconfiguration information may be transferred to the user equipmenteither when an RRC connection is setup between the base station and userequipment or when the RRC connection is released.

The user equipment 105 logs MDT measurements when a logging criterion issatisfied during MDT measurement (150). Here, it may be not reasonablefor the user equipment 105 to consider all the logging criteria duringMDT measurement. For example, since power headroom is measurable only inconnected mode, the logging criterion “Transmit power headroom becomesless than threshold” may be satisfied only in connected mode.

Hence, basic MDT operations may be classified according to operationmodes in consideration of usefulness and ease of implementation asillustrated in Table 2.

TABLE 2 Idle mode: Connected mode: MDT measurements logged reportingimmediate reporting Periodic downlink pilot Yes No measurements Servingcell becomes worse Yes No than threshold Transmit power headroom No Yesbecomes less than threshold Random access failure Yes No Paging channelfailure Yes No Broadcast channel failure Yes No Radio link failurereport No Yes

Basic MDT operations classified by RRC state

In general, existing RRC measurements obtained in connected mode mayinclude most MDT measurements. In connected mode, desired channelmeasurement information may be obtained using existing RRC measurementsexcept for those related to “Transmit power headroom becomes less thanthreshold” and “Radio link failure report”. If the same process is notrepeated, only MDT measurements related to these two events arecollected in connected mode. Hence, the amount of MDT measurementscollected in connected mode is unlikely to be large. On the contrary, inidle mode, as RRC measurements are not obtained, most MDT measurementshave to be collected. As the user equipment remains in idle mode for atime much longer than that in connected mode, the amount of MDTmeasurements collected in idle mode is likely to be larger than thatcollected in connected mode.

The user equipment 105 stops MDT measurement when the specified timeexpires (155).

Thereafter, the user equipment 105 determines to transition to connectedmode (160) and sends an RRCConnectionRequest message to the base station110 (165). When the base station 110 accepts the request, it sends anRRCConnectionSetup message to the user equipment 105 (170).

After transitioning to connected mode, the user equipment 105 maytransfer channel measurement information logged in idle mode to the basestation 110. To transfer channel measurement information, the userequipment 105 sends an RRCConnectionSetupComplete message containingindex information of the logged channel measurement information to thebase station 110 (175). The index information may include:

(1) Amount of logged measurement information

(2) Event related to MDT measurement (for example, random access failureor other)

(3) Elapsed time after logging

(4) MDT configuration applied to MDT measurement

(5) Others.

Such index information notifies the base station 110 of the type ofchannel measurement information logged in the user equipment 105 so thatthe base station 110 may determine whether to issue a report request forthe logged channel measurement information.

For example, when the user equipment 105 remains in idle mode for a longtime, it may log a large amount of channel measurement information. Upontransitioning to connected mode, the user equipment 105 may have toconsume a lot of resources to send the channel measurement information.To overcome this problem, the base station 110 requests necessaryinformation only on the basis of index information.

When the channel measurement information logged in the user equipment105 is necessary, the base station 110 sends a UEInformationRequestmessage containing an MDT report request to the user equipment 105(180).

Upon reception of the UEInformationRequest message, the user equipment105 triggers reporting of MDT measurement information after the lastdata radio bearer (DRB) related to regular data is released (185). Thisis because regular data has a higher priority than logged measurementinformation. That is, logged measurement information need not be sentimmediately. Alternatively, a separate radio bear with a low prioritymay be established to transmit MDT measurement information.

The user equipment 105 sends a UEInformationResponse message containingthe MDT measurement information to the base station 110 (190).

Second Embodiment

FIG. 2 is a sequence diagram illustrating a procedure for reportingchannel measurement information by a user equipment (UE) 205 to a basestation (eNB) 210 in response to satisfaction of a report triggeringcondition.

Steps 215 to 275 of FIG. 2 are identical respectively to steps 115 to175 of FIG. 1, and a description thereof is thus omitted.

In the second embodiment, unlike the first embodiment, the userequipment 205 may send logged MDT measurement information, when aspecific condition is satisfied, without a report request from the basestation 210.

Here, the condition may correspond to any reporting criterion other than“on demand”. For example, the user equipment 205 may send loggedmeasurement information to the base station 210 at a preset time or whenthe memory buffer is nearly full. However, measurement information sentby triggering such a reporting criterion may be information that is notreally needed by the base station 210.

To prevent this, the base station 210 may reject reporting ofmeasurement information on the basis of index information contained inthe RRCConnectionSetupComplete received from the user equipment 205.That is, referring to FIG. 2, when the measurement information is notnecessary, the base station 210 sends a UEInformationRequest containinga report rejection indication to the user equipment 205 (280).

When the received UEInformationRequest contains a report rejectionindication, the user equipment 205 ignores triggering of MDT reportingcaused by satisfaction of a corresponding reporting criterion. Here, toidentify the intentions of the base station 210, the user equipment 205may defer MDT measurement reporting for a preset time after transmissionof the RRCConnectionSetupComplete message.

When MDT measurement reporting is accepted by receiving aUEInformationRequest containing an MDT report request or no informationis received from the base station 210 for a preset time, the userequipment 205 triggers MDT reporting (285) and sends the MDT measurementinformation to the base station 210 in consideration of transmissionpriority (290).

FIG. 3 is a flow chart illustrating steps performed by the userequipment 105 conducting MDT operation.

Referring to FIG. 3, when an RRCConnectionReconfiguration message isreceived from the base station 110, the user equipment 105 extracts MDTconfiguration information from the received message (310). As a reply,the user equipment 105 sends an RRCConnectionReconfigurationCompletemessage to the base station 110 (315).

When the MDT measurement time indicated by the MDT start/stopconfiguration of the MDT configuration information is reached (320), theuser equipment 105 starts MDT measurement and logs measurement resultsupon satisfaction of a logging event (325).

Thereafter, the user equipment 105 determines necessity of transitioningfrom idle mode to connected mode (330). When transitioning to connectedmode is necessary, the user equipment 105 sends an RRCConnectionRequestmessage to the base station 110 (335). As a reply, the base station 110sends an RRCConnectionSetup message to the user equipment 105 (340).

As a reply to the RRCConnectionSetup message, the user equipment 105sends an RRCConnectionSetupComplete message containing index informationof the logged MDT measurement information to the base station 110 (345).

When the logged MDT measurement information is determined to benecessary after examining the index information, the base station 110sends a UEInformationRequest message containing an MDT report request tothe user equipment 105 (350). Upon reception of the UEInformationRequestmessage containing an MDT report request, the user equipment 105 sends aUEInformationResponse message containing the logged MDT measurementinformation to the base station 110 (355).

When the received UEInformationRequest contains a report rejectionindication, the user equipment 105 defers reporting of the MDTmeasurement information (360). Here, if the user equipment 105 has areport triggering condition separate from a report request, it may sendMDT measurement information upon triggering of the report triggeringcondition when a report request is received from the base station 110 ora report rejection indication is not received. Alternatively, when areport rejection indication is received from the base station 110, theuser equipment 105 may ignore triggering of the report triggeringcondition and defer reporting.

FIG. 4 is a flow chart illustrating steps performed by the base station110 conducting MDT operation.

Referring to FIG. 4, for MDT operation, the base station 110 sends anRRCConnectionReconfiguration message containing MDT configurationinformation to the user equipment 105 (410). When theRRCConnectionReconfiguration message is successfully received, the userequipment 105 sends an RRCConnectionReconfigurationComplete message tothe base station 110. The base station 110 receives theRRCConnectionReconfigurationComplete message (415).

When data to be sent is present, the user equipment 105 sends anRRCConnectionRequest message to the base station 110. The base station110 receives the RRCConnectionRequest message (420) and sends, as areply, an RRCConnectionSetup message to the user equipment 105 (425).

As a reply to the RRCConnectionSetup message, the user equipment 105sends an RRCConnectionSetupComplete message containing index informationof logged measurement information to the base station 110. The basestation 110 receives the RRCConnectionSetupComplete message (430) anddetermines whether the measurement information logged in the userequipment 105 is necessary (435).

When the logged measurement information is necessary, the base station110 sends a UEInformationRequest message containing a report request tothe user equipment 105 (440). Later, the base station 110 receives aUEInformationResponse message containing the MDT measurement informationfrom the user equipment 105 (445).

When the logged measurement information is not necessary, the basestation 110 sends a UEInformationRequest message containing a reportrejection indication to the user equipment 105 (450).

Here, when the user equipment 105 has enabled the “on demand” reportingcriterion, the base station 110 does not have to separately notify areport rejection indication to the user equipment 105. This is becausethe user equipment 105 having enabled the “on demand” reportingcriterion sends a measurement report only when the base station 110issues a request.

Third Embodiment

FIG. 5 is a sequence diagram illustrating a procedure for reportingchannel measurement information in which a user equipment 505 notifies abase station 510 of collected channel measurement information and sendsthe channel measurement information according to a report request fromthe base station 510.

Steps 515 to 570 of FIG. 5 are identical respectively to steps 115 to170 of FIG. 1, and a description thereof is omitted.

To transition from idle mode to connected mode, the user equipment 505has to perform RRC connection establishment, which corresponds to steps565 to 575 of FIG. 5. In the first and second embodiments, the userequipment provides index information of channel measurement informationto the base station during RRC connection establishment. This means amodification to the existing RRC connection establishment operation.

The user equipment may also send logged channel measurement informationto the base station without modification to the existing RRC connectionestablishment operation (corresponding to steps 565 to 575),contributing to reduction of system complexity and overhead.

To achieve this, in the third embodiment, the user equipment 505notifies the base station 510 of logged MDT measurement informationduring RRC connection establishment. That is, the user equipment 505sends an RRCConnectionSetupComplete message containing a flag (575).Here, the flag informs the base station 510 of MDT measurementinformation logged in the user equipment 505. For example, the flag setto ‘0’ may indicate absence of logged MDT measurement information andthe flag set to ‘1’ may indicate presence of logged MDT measurementinformation.

When an RRCConnectionSetupComplete message containing a flag set to ‘1’is received, the base station 510 requests the user equipment 505 tosend MDT measurement information in the following two stages.

First, to prevent accumulation of unnecessary channel measurementinformation, the base station 510 sends a request for index informationof MDT measurement information to the user equipment 505 (580). Asdescribed before in connection with the first embodiment, the indexinformation may include:

(1) Amount of logged measurement information

(2) Event related to MDT measurement (for example, random access failureor other)

(3) Elapsed time after logging

(4) MDT configuration applied to MDT measurement

(5) Others.

The base station may use a UEInformationRequest message to request indexinformation and use a UEInformationResponse message to collect indexinformation.

Second, the base station 510 analyzes the received index information todetermine necessity of the MDT measurement information logged in theuser equipment 505; and, when the logged MDT measurement information isnecessary, the base station 510 sends a UEInformationResponse messagecontaining a report request to the user equipment 505 (585). When areport request is issued by the base station 510, the user equipment 505triggers reporting of the MDT measurement information (590) and sends aUEInformationResponse message containing the MDT measurement informationto the base station 510.

Fourth Embodiment

FIG. 6 is a sequence diagram illustrating a procedure for reportingchannel measurement information derived from the third embodiment ofFIG. 5 by replacing a two-step report requesting operation with asingle-step operation.

As in the third embodiment, the user equipment 605 sends anRRCConnectionSetupComplete message containing a flag to the base station610 (675). Here, the flag informs the base station 610 of MDTmeasurement information logged in the user equipment 605. The flag setto ‘0’ indicates absence of logged MDT measurement information and theflag set to ‘1’ indicates presence of logged MDT measurementinformation.

When an RRCConnectionSetupComplete message containing a flag set to ‘1’is received, the base station 610 sends, if necessary, aUEInformationRequest message to request the user equipment 605 totransfer the MDT measurement information (680). The user equipment 605sends a UEInformationResponse message containing the MDT measurementinformation and the following information to the base station 610 (690).

(1) MDT configuration applied to MDT measurement

(2) Others.

As channel measurement information is also sent to the base station 610in the fourth embodiment, items (1) to (3) of the index information ofMDT measurement information in the third embodiment may be unnecessary.

Fifth Embodiment

FIG. 7 is a sequence diagram illustrating a procedure for reportingchannel measurement information in which a user equipment 705 notifies abase station 710 of collected channel measurement information using twoflags and sends the channel measurement information according to areport request from the base station 710.

It is necessary for the base station 710 to identify whether the userequipment 705 has completed MDT measurement according to a specific MDTconfiguration. While the user equipment 705 is performing MDTmeasurement, it is unnecessary for the base station 710 to requesttransmission of MDT measurement information. When the user equipment 705has completed MDT measurement, the base station 710 may request the userequipment 705 to send logged MDT measurement information or may requestthe user equipment 705 to change the MDT configuration (reconfiguration)for new MDT measurement.

To achieve this, the user equipment 705 sends anRRCConnectionSetupComplete message containing two flags to the basestation 710 (775). Here, the first flag indicates presence of MDTmeasurement information as in the third embodiment. That is, when MDTmeasurement information is not present, the first flag is set to ‘0’;and when MDT measurement information is present, the first flag is setto ‘1’. The second flag indicates completion of MDT measurement. Thatis, when the user equipment 705 is conducting MDT measurement, thesecond flag is set to ‘0’; and when the user equipment 705 has completedMDT measurement, the second flag is set to ‘1’. When none of the loggingcriteria are satisfied while the user equipment 705 is conducting MDTmeasurement according to configuration information received from thebase station 710, measurement information may be not collected.

Table 3 shows an example of base station operations corresponding to thevalue of the two flags.

TABLE 3 Two flags MDT performance BS operation 00 Consider that UE islogging nothing even Not demand and though MDT was configured. Andconsider Not reconfigure UE as still performing MDT configuredpreviously. 10 Consider that MDT was configured and UE Not demand andhas logged measurement. And consider UE Not reconfigure as stillperforming MDT configured previ- ously. 01 Consider that UE is loggingnothing even Not demand though MDT was configured, or UE was notandPossible to configured. And consider that it is possible reconfigureto configure or reconfigure MDT. 11 Consider that MDT was configured andUE Possible to demand has logged measurement. And consider that andPossible to it is possible to reconfigure MDT. reconfigure

Base station operations corresponding to flag values

When the flags are set to ‘00’, the base station 710 regards the userequipment 705 as having no logged channel measurement information and asconducting previously configured MDT measurement, and neither requestsan MDT report nor reconfigures MDT measurement. When the flags are setto ‘10’, the base station 710 regards the user equipment 705 as havinglogged channel measurement information and as conducting previouslyconfigured MDT measurement, and does not perform an MDT related action.When the flags are set to ‘01’, the base station 710 regards the userequipment 705 as having no logged channel measurement information and asnot conducting MDT measurement, and does not requests an MDT report butmay reconfigure MDT measurement. When the flags are set to ‘11’, thebase station 710 regards the user equipment 705 as having logged channelmeasurement information and as not conducting MDT measurement, and mayrequest an MDT report and reconfigure MDT measurement.

When the flags are set to ‘11’, the user equipment 705 may be regardedas having completed MDT measurement as directed. In this case, the basestation 710 may send a UEInformationRequest message containing a reportrequest to the user equipment 705 (780). When MDT reporting isrequested, the user equipment 705 triggers reporting (785) and send aUEInformationResponse message containing the MDT measurement informationand the following information to the base station 710 (790).

(1) MDT configuration applied to MDT measurement

(2) Others

For the user equipment 705 having completed MDT measurement as directed,if necessary, the base station 710 may send anRRCConnectionReconfiguration message to the user equipment 705 for newMDT measurement (795).

FIG. 8 is a block diagram of a user equipment (UE) 105 conducting MDToperation. As shown in FIG. 8, the user equipment 105 may include acontroller 805, a buffer 810 and a transceiver 815.

The transceiver 815 sends and receives RRC-messages to and from the basestation 110, and performs channel measurement under control of thecontroller 805. A received RRC-message is forwarded to the controller805 and used to control operations of the user equipment 105.

The controller 805 performs channel measurement and collects channelmeasurement information if needed. In this case, as shown in Table 2,the controller 805 may selectively trigger an event for logging channelmeasurement information according to the state of connection with thebase station 110. The controller 805 logs collected channel measurementinformation in the buffer 810 according to the triggered logging event.The controller 805 controls an operation to transfer index informationof logged channel measurement information to the base station 110. Here,the index information may include at least one of the amount of loggedmeasurement information, events related to MDT measurement, the elapsedtime after logging and the MDT configuration applied to MDT measurement.In an embodiment, as to transmission, logged channel measurementinformation may have a lower priority than regular data. In anotherembodiment, the controller 805 may establish a separate radio bearerwith a low priority to transmit channel measurement information to thebase station 110.

The controller 805 controls an operation to transmit channel measurementinformation to the base station 110 according to a request from the basestation 110 or an internal criterion. For transmission, the controller805 may assign a lower priority to channel measurement information thanthat of regular data.

In the second embodiment, the controller 805 may provide indexinformation to the base station and then receive a report rejectionindication from the base station. In this case, the controller 805 mayignore triggered reporting of channel measurement information.

In the third embodiment, the controller 805 may provide a flag thatindicates presence of logged channel measurement information to the basestation. The base station may send a request for index information ofthe channel measurement information. When a request for indexinformation is received, the controller 805 sends the index informationto the base station.

In the fourth embodiment, the controller 805 may provide a flag thatindicates presence of logged channel measurement information to the basestation. When a request is received, the controller 805 may send thechannel measurement information to the base station. In this case, indexinformation of channel measurement information may be not delivered tothe base station.

In the fifth embodiment, the controller 805 may provide a first flagindicating presence of logged channel measurement information and asecond flag indicating completion of MDT measurement to the basestation. The controller 805 may perform other operations in the same wayas in the third or fourth embodiment described above.

The buffer 810 stores collected channel measurement information, andsends the same through the transceiver 815 to the base station 110 undercontrol of the controller 805.

FIG. 9 is a block diagram of a base station (eNB) 110 conducting MDToperation. As shown in FIG. 9, the base station 110 may include atransceiver 905 and a controller 910.

The transceiver 905 sends and receives RRC-messages to and from the userequipment 105 and receives MDT measurement information from the userequipment 105.

The controller 910 controls operations of the base station according toembodiments. In particular, the controller 910 may deliver MDTconfiguration information to the user equipment at theRRCConnectionReconfiguration stage. The MDT configuration informationmay include information regarding an MDT measurement time, a frequencyband and cell to be measured, and logging and reporting of measurements.

The controller 910 may identify index information of channel measurementinformation received from the user equipment and determine whether toissue a report request. When the channel measurement information isnecessary, the controller 910 may control an operation to send a reportrequest to the user equipment. When the user equipment sends the channelmeasurement information in response to the report request, thecontroller 910 may receive the channel measurement information.

In the second embodiment, the controller 910 may receive channelmeasurement information from the user equipment at a specified time.When channel measurement information from the user equipment is notnecessary, the controller 910 may deliver a report rejection indicationto the user equipment.

In the third embodiment, the controller 910 may receive a flagindicating presence of logged channel measurement information from theuser equipment. The controller 910 checks the flag to determine whetherto issue a request for index information of channel measurementinformation. If necessary, the controller 910 requests the userequipment to send the index information. The controller 910 checks thereceived index information to determine whether to issue a reportrequest. If necessary, the controller 910 may request the user equipmentto send the channel measurement information.

In the fourth embodiment, the controller 910 may receive a flagindicating presence of logged channel measurement information from theuser equipment and check the flag to determine whether to issue a reportrequest. If necessary, the controller 910 requests the user equipment tosend the channel measurement information.

In the fifth embodiment, the controller 910 may receive a first flagindicating presence of logged channel measurement information and asecond flag indicating completion of MDT measurement from the userequipment. The controller 910 may perform other operations in the sameway as in the third or fourth embodiment described above.

1. A method of transmitting channel measurement information for a userequipment in a mobile communication system, comprising: receiving MDTconfiguration information from a corresponding base station; performing,upon transitioning to idle mode, MDT measurement for channel statusaccording to the MDT configuration information and logging MDTmeasurement information; sending, upon transitioning to connected mode,a flag indicating presence of the logged MDT measurement information tothe base station; and sending, upon reception of a report request fromthe base station, the MDT measurement information to the base station.2. The method of claim 1, wherein transmission of the MDT measurementinformation is performed with a lower priority than transmission ofregular data.
 3. The method of claim 1, wherein sending the MDTmeasurement information to the base station comprises: establishing aradio bearer having a lower priority than that of a radio bearer forregular data; and transmitting the MDT measurement information via theestablished radio bearer.
 4. The method of claim 1, further comprising:determining, upon reception of the flag by the base station, necessityof the MDT measurement information; and sending, when the MDTmeasurement information is needed by the base station, aUEInformationRequest message containing a request for the MDTmeasurement information to the user equipment.
 5. The method of claim 1,wherein the MDT configuration information comprises informationregarding at least one of an MDT measurement time, a frequency or cellto be measured, and a measurement logging or reporting time.
 6. A userequipment transmitting channel measurement information in a mobilecommunication system, comprising: a transceiver receiving MDTconfiguration information from a corresponding base station and sendingMDT measurement information to the base station; a buffer storingcollected MDT measurement information; and a controller controlling aprocess of performing, upon transitioning to idle mode, MDT measurementfor channel status according to the MDT configuration information andlogging MDT measurement information in the buffer, sending, upontransitioning to connected mode, a flag indicating presence of thelogged MDT measurement information to the base station, and sending,upon reception of a report request from the base station, the MDTmeasurement information to the base station.
 7. The user equipment ofclaim 6, wherein transmission of the MDT measurement information isperformed with a lower priority than transmission of regular data. 8.The user equipment of claim 6, wherein the controller controls, fortransmission of MDT measurement information, an operation to establish aradio bearer having a lower priority than that of a radio bearer forregular data and to transmit the MDT measurement information via theestablished radio bearer.
 9. The user equipment of claim 6, wherein thebase station uses the flag to determine necessity of the MDT measurementinformation, and requests, when the MDT measurement information isneeded, reporting of the MDT measurement information by sending aUEInformationRequest message.
 10. The user equipment of claim 6, whereinthe MDT configuration information comprises information regarding atleast one of an MDT measurement time, a frequency or cell to bemeasured, and a measurement logging or reporting time.